Reverse membrane filtration

Membrane Filtration. Membrane filtration describes a number of weU-known processes including reverse osmosis, ultrafiltration, nanofiltration, microfiltration, and electro dialysis. The basic principle behind this technology is the use of a driving force (electricity or pressure) to filter... 

The individual membrane filtration processes are defined chiefly by pore size although there is some overlap. The smallest membrane pore size is used in reverse osmosis (0.0005—0.002 microns), followed by nanofiltration (0.001—0.01 microns), ultrafHtration (0.002—0.1 microns), and microfiltration (0.1—1.0 microns). Electro dialysis uses electric current to transport ionic species across a membrane. Micro- and ultrafHtration rely on pore size for material separation, reverse osmosis on pore size and diffusion, and electro dialysis on diffusion. Separation efficiency does not reach 100% for any of these membrane processes. For example, when used to desalinate—soften water for industrial processes, the concentrated salt stream (reject) from reverse osmosis can be 20% of the total flow. These concentrated, yet stiH dilute streams, may require additional treatment or special disposal methods. 

Membrane filtration processes, such as reverse osmosis, and micro and ultra filtration, are used to filter out dissolved solids in certain applications see Table 10.9. These specialised processes will not be discussed in this book. A comprehensive description of the techniques used and their applications is given in Volume 2, Chapter 8 see also Scott and Hughes (1995), Cheryan (1986), McGregor (1986) and Porter (1997). 

Recently, membrane filtration has become popular for treating industrial effluent. Membrane filtration includes microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse... 

In addition to these three treatments, there are several alternative treatment technologies applicable to the treatment of common metals wastes. These technologies include electrolytic recovery, electrodialysis, reverse osmosis, peat adsorption, insoluble starch xanthate treatment, sulfide precipitation, flotation, and membrane filtration.1516... 

In the field of membrane filtration, a distinction is made based upon the size of the particles, which are retained by the membrane. That is micro-, ultra-, nanofiltration and reverse osmosis. Figure 4.8 shows a schematic picture of the classification of membrane processes. The areas of importance for application with homogeneous catalysts are ultra- and nanofiltration, depicted in gray. 

Membrane filtration (reverse osmosis, nanofiltration, ultrafiltration, microfiltration)... 

Koyuncu et al. [56] presented pilot-scale studies on the treatment of pulp and paper mill effluents using two-stage membrane filtrations, ultrafiltration and reverse osmosis [56]. The combination of UF and RO resulted in very high removals of COD, color, and conductivity from the effluents. At the end of a single pass with seawater membrane, the initial COD, color and conductivity values were reduced to 10-20 mg/L, 0-100 PCCU (platinum cobalt color units) and 200-300 ps/cm, respectively. Nearly complete color removals were achieved in the RO experiments with seawater membranes. 

In summary, water can be a source of contaminants. If the raw material (drinking water) complies with the quahty parameters established by authorities, contaminants still present can be eliminated by usual water purification processes available to the pharmaceutical industry. While distillation and reverse osmosis provide water with the quality specifications for purified water and highly purified water, WFI is generally obtained by membrane filtration (associated with another purification process) not only because of chemical contamination but mainly because of sterility requirements. 

There are five basic water purification technologies—distillation, ion exchange, carbon adsorption, reverse osmosis, and membrane filtration. Most academic laboratories are equipped with in-house purified water, which typically is produced by a combination of the above purifying technologies. For most procedures carried out in a biochemistry teaching laboratory, water purified by deionization, reverse osmosis, or distillation usually is acceptable. For special procedures such as buffer standardization, liquid chromatography, and tissue culture, ultrapure water should be used. 

Concentration Units. Typical concentrators for rinsing solutions are membrane filtration units, which split the feed into diluate and concentrate streams, meaning purification and recovery, respectively [106], Both nanofiltration and reverse osmosis might be applied, depending on the physico-chemical properties of the solutes. 

Polymeric membranes also have vast applications in several processes, such as desalination using reverse osmosis membranes. Filtration, in a wide sense, with polymeric membranes can be applied in gas separation processes, biochemical processing, wastewater treatment, food and beverage production, and pharmaceutical applications [59-61],... 

This chapter continues the discussion on hltration started in Chapter 7, except that it deals with advanced hltration. We have dehned filtration as a unit operation of separating solids or particles from huids. A unit operation of hltration carried out using membranes as hlter media is advanced hlhation. This chapter discusses advanced hlhation using elechodialysis membranes and pressure membranes. Filtration using pressure membranes include reverse osmosis, nanohlhation, microhltration, and ultrahltration. 

Evaporation, reverse osmosis (membrane filtration at high pressure)... 

Reverse osmosis offers the possibility of achieving more than one purification purpose in one step. It simultaneously reduces the hardness and the concentration of other salts, as well as organic molecules, bacteria or viruses. The higher the concentration of undesired ingredients in the well water, the more economic the membrane filtration becomes as compared to the ion exchange treatment. RO for water purification is one of the oldest applications of membrane separation and has been extensively discussed in literature over the years. 

Filtration membrane filtration is a common process that is widely used in many industries. The examples of membrane filtration include microfiltration, ultrafiltration, nanofiltration, reverse osmosis, and the newly developed technology such as hydrophobic membrane. 

The influence of metal oxide derived membrane material with regard to permeability and solute rejection was first reported by Vernon Ballou et al. [42,43] in the early 70s concerning mesoporous glass membranes. Filtration of sodium chloride and urea was studied with porous glass membranes in close-end capillary form, to determine the effect of pressure, temperature and concentration variations on lifetime rejection and flux characteristics. In this work experiments were considered as hyperfiltration (reverse osmosis) due to the high pressure applied to the membranes, 40 to 120 atm. In fact, results reproduced in Table 12.3 show that these membranes do not behave as h)qjerfiltra-tion membranes but as membranes with intermediate performances between ultra- and nanofiltration in which surface charge effect of metal oxide material plays an important role in solute rejection. 

---